Electric heating pad



June 13, 1939. w. w. SMITH 2,162,287

ELECTRIC HEATNG PAD Filed Nov. 5, 1938 /di Z.

Patented June 13, 12939 UNITED STATES PATENT OFFICE 5Clalms.

This invention relates to improvements in electric heating pads or appliances used for therapeutic purposes, and particularly to that type of such devices which have a substantially rigid casing or outer shell. I

The objects of the invention are to construct an electric heating pad of the kind mentioned which is of relatively inexpensive and durable construction, is light in weight and has a smooth 0 uniform outer surface substantially without projections and which is so constructed as to be easily and quickly taken apart for inspection, re-

moval and replacement of parts; also to provide an electric heating pad having an electric heating element therein provided with a relatively large insulating and heat storing covering so arranged that said element and covering are surrounded by a substantial air space between the same and the casing or shell of the pad so as to thereby reduce to a minimum the possibilities of users receiving burns when the pad is at a high temperature; also to provide a pad having a casing formed of two half shells of substantially like construction having therein integral parts for spacing or locating the heating element and its insulation in correct operative position and in which means are provided for ilrmly clamping the element and its insulation in correct position and in spaced relation to the walls of the shell; also to provide a pad of this kind with a thermostatic device for controlling the temperature of the heating element and which is contained entirely within the chamber formed between the half shells and in spaced relation to the heating element and to the marginal portions of the casing; also to construct a pad of this kind having a casing of relatively rigid molded material which acts as an insulator against the passage of electric 'current therethrough and in which means are provided for detachably connecting the contacts of an electric plug or device thereto in a manner to enable current to be supplied to the heating device by way of the thermostat and so that after the pad has been heated to the required extent, the pad may be disconnected from the source of current before the pad is placed in use so that no danger from electric shock is possible to the person using the device; and also to arrange the pad with contact receiving sleeves or parts vhlch are permanently enveloped or molded in the insulating material of which the casing is formed.

Various other objects and advantages of the invention will be apparent from the following disclosure of an embodiment thereof, and its novel (Cl. 21S-19) features-will be pointed out in connection with the appended claims.

In the drawing: V

Fig. 1 is an inside face or plan View of one of the half shells of an electric heating pad constructed in accordance with this invention, showing a heating element and a thermostat in operative position therein, certain parts of the pad being in section.

Fig. 2 is a longitudinal section of the pad taken approximately on the line 2 2 of Fig. 1.

Fig. 3 is a transverse section of the pad on the line 3 3 of Fig. 1.

Fig. 4 is an outside face view of the pad.

Fig. 5 is a sectional view illustrating the construction of a suitable thermostat for use in the pad.

Fig. 6 is a fragmentary end elevation of the pad showing the two half shells thereof partly separated and illustrating the manner of securing the contact receiving sleeves in place.

Fig. 7 is a fragmentary cross sectional view taken on the line 1 1, Fig. 2, showing the manner of securing the thermostat in position.

In the embodiment of the invention illustrated in the drawing, my improved electric heating pad comprises a relatively at and shallow, approximately rectangular shell A which is formed' of two substantially similar half shells or sections II and II. These half shells may be formed of any suitable material but preferably they are made of a material which may be molded into the desired form, such as Bakelite or other plastic material, although materials of other type adapted to be molded may be used, if desired. Each of the half shells 4Il and II includes a substantially ilat wall or part I2 merging into curved marginal flanges or shallow side wall portions I3 terminating in flat edges Il which extend substantially continuously entirely around the shell so that when the parts are assembled, the edges I4 engage to close the shell A, which thus has formed within it a closed space or chamber I5.

The two half shells I0 and Il may be secured together in any suitable way to form the complete shell A, preferably so that the two shells may be easily and quickly separated when desired. For this purpose, in the construction illustrated, I provide each half shell with a plurality of bosses or projections I6 extending inwardly from the opposite side anges I3 and integral therewith and with the adjacent portions of the wall I2. In each boss on one of the shells as, forY example, the shell Il, I provide a threaded bushing I'l which is permanently molded in place and is positioned to receive a screw or fastening device I8, the shank of which passes through a registering hole in the corresponding lug or boss I6, on the other half shell Il, and the head of which is engaged in a recess or countersunk opening at the outer side or face of the half shell Il.

It will be noted, upon examination of Fig. 3, that the opposed inner faces of the bosses I6 are set back or are disposed slightly below the plane of the edges i4 of the half shells so that these bosses are out of contact when the two half shells are assembled. Thus the margins I4 of the shells may firmly engage and form a tight closure entirely around the sides of the pad.

As shown clearly in Figs. 1 to3, I arrange within the space or chamber I5 of the shell A orcasing an electric heating element 20 which may be of anyusual or suitable construction, such as may be readily purchased in the open market, and

which is of substantially flat rectangular form. The heating element 20 may consist of the usual micron wires or ribbons 2| disposed between opposed layers of mica or other insulating material 22 which, in turn, is enveloped in a sheet of suitable metal or other relatively rigid material 23.

Portions 24 and 25 of the mrcon wire may extend as usual from one end of the heater for attachment to the source of electrical current, as is well known.`

In order to provide means for absorbing and storing heat generated in the heating element 20, I engage with or apply to each of the fiat faces of the element 20 a slab or sheet of insulating material 25 which may be formed of asbestos compound of any usual or well known commercial form, and the thickness of which is such that vthe combined thickness of these slabs 25 plus that of the element 20 is apprecably less than the space between the opposed flat inner walls of the connected half shells I0 and Il. In order to support and maintain these parts in such spaced relation to the inner faces of the half shells, I provide means whereby, when the two half shells are secured together, the element and the insulating members 25 are firmly clamped in position. For this purpose, I place between the outer faces of the two insulating slabs 25 and the adjacent inner facesv of the half shells small narrow strips 30 of suitable material which can be slightly compressed by the half shells l0 and H so as to firmly grip and frictionally hold the parts ln position when the half shells are secured together. Any suitable material may be used for this purpose, the strips 30 being conveniently formed of pieces of insulating material similar to that of which the slabs 25 are formed. It will be seen upon inspection of Figs. 21 and 3 that by this arrangement the heating element 20 and its heat storing and insulating members 25 are firmly and securely mounted in position in spaced relation to the inner flat faces and side andI end marginal portions of -the shell A.

In this way, ample air space is providedbetween the heat storing elements and the shell A of the pad so that possibility of burning of the person using the device is reduced to a minimum, while atvthe same time enabling ample heat to be transferred to the shell so that suilicient heat may be available when the device is in use.

Upon reference to Figs. 1 and 3, it will be noted that the inwardly facing or oppositely disposed ends or faces of the bosses I6 on the half shells are in alignment at opposite sides of the pad, and these faces form shoulders or abutments whereby the heating element 20 and the insulating slabs 25 may be centered or accurately positioned i correct relation to the shells. If desired, the opposed pairs of bosses I6 of each half' shell may be connected by a transverse rib or corrugation 32 which tends to stiften the half shells and prevent flexing of these parts under the weight of a person using the pad.

As shown in the drawing, I provide the shell A with novel means of simple construction for enabling the contacts of an electric plug or cord to be secured to the shell for the purpose of conducting electricity to the element V2li for heating the pad. For this purpose, I provide at one end of one of the half shells, for example, half shell l0, an inwardly extending boss or portion 35 which is preferably formed integrally with that half shell, and within this boss 35 I permanently mold orsecure a pair of metal conducting sleeves or members 35, as shown. The outer ends of these sleeves 36 are flush with the outer face of the half shell. I6 and the other ends of the sleeves may project inwardly beyond the boss 35 for connection thereto, as by screws 31, of the conductors by which current is carried from the sleeves to the heating element 20.

Any suitable attachment may be made between the paid and the source of electrical energy such vas by means of a pair of pins 39 which project from a plug 40 to which is secured the usual cord 4l, the opposite end of which, not shown, can be connected with an outlet to receive current therefrom.

While, if desired, the conductors 24 from the element 20 may be connected directly to the sleeves 3,6, I prefer to interpose an adjustable thermostatic device, such as that shown generally at 42, whereby the current is supplied to the element 20 Athrough the thermostat and so that after' the interior of the pad has reached a desired temperature, a circuit will be opened to disconnect the current from the element 20.

In this way, the pad, or a number of the pads, may be placed upon a suitable support and connected to a source of current in the manner eX- plained whereupon, in a short time, the pads will become heated to the desired temperature, and whereupon the thermostatic device 42 in each pad will act to open the circuit of that pad and cut olf the supply of current. When heated to the desired extent, each pad \can be disconnected from its cord and placed in use, thus enabling the pad to be used while disconnected from the cord andthe source of electric current so that the utmost safety in use is assured.

By this arrangement too, an attendant can connect a number of the pads to a source of current for heating the pads, as in a hospital Where a number of such pads may be needed at one time, and then attend other duties with the assurance that the pads, after being heated to the desired extent, will be automatically disconnected from thev source of current by their thermostats so as to thereby avoid over-heating, while should the attendant remain away for such time that the pads begin to cool, the thermostatic device in each pad will act to close the circuit and again supply the element 20 with current to reheat the pad. In this way, all of the pads will be heated to the required extent when they are needed.

'I'he thermostatic element 42 may be of any suitable or desired construction, the one shownV illustrated the thermostate device 42 in detail in l Fig. 5, but it should be understood that this thermostatic device 42, per se, forms no part of the invention andi any other f orm oi' thermostatic device, preferably adjustable, may be used in its stead.

'l'he thermostat 42 includes an elongated shell or box 4J upon which is mounted and properly insulated a pair of binding posts 44 and 45. One oi' the contact posts, as for example the post 44, is connected to a bimetallic thermostatic strip or element 48 which is suitably mounted in the box 43 upon an insulating block 41 and is provided at its free end with a contact 48. 'I'he other binding post 45 is connected to acontact strip 49 in the box 43 and is provided with a contact 5I on its free end which is normally in engagement with the contact 4I of the bimetallic strip 48. Thel posts 44 and 4l are also adapted to have secured to them a conductor or wire 5I, and one of the wires 24 respectively, while the other wire 24 is secured to a conductor Ila. The conductors 5i, Ila in turn are secured to the sleeves J6 by means of -the screws Il, as before explained, thus ccman electric circuit between the `element 20 an the source of supply when the pins Il are en gaged in the sleeves 3l. l l With the current flowing through the circuit' described, the element 2l will beheated, and upon a desired temperature being attained in the pad or casing A, the bimetallic thermostat` strip 46 will be caused ,to move its contact away from the contact l0, thus opening the'cir- .v cuit and preventing overheating of the pad. In order to vary the temperature within limits, the contact strip 4! may be moved towards and from the strip 46, as byl means of an adjusting screw l2, mounted upon the casing 4I of the thermostatic device 42 and having at its inner end an insulating pin Il which bears against the strip 4I. By adjusting the screw 52 in one direction or another change in the tension of the strip 4! against the strip 46 may be secured, as is well known in the art.

'I'he thermostatic device 42 may be mounted within the shell A in any suitable'way. For example, as shown in Figs. l and 7, the box 43 of the device is provided with a pair of oppositely extending lugs 54 which are apertured for the reception of screws I! which may be engaged in threaded bushings I6 molded permanently into upstanding bosses l1 formed upon the inner face of the half shell Il. However, the element 42 may be secured in any suitable way.

It will be seen upon reference to Fig. 6 that the boss 35 is formed entirely upon the half shell i0 and projects partly above the adjacent margin i4 thereof so that the conducting sleeves entirely and permanently enveloped in the material of which that shell is made, thus forming a simple and secure attachment of the sleeves in the shell. In order to enable the shells I0 and I I to be connected together, as described, the adjacentk iiange or marginal wall portion Il of the other half shell II is urecessed as shown at 58 so that when lthe two half shells are brought together, the projecting portion of the boss 35 will seat in the recess 58 and in this way, no openings into the casing` or shell A are formed.

I claim as my invention: l

l. In an electric'heating pad, a pair of shallow substantially rectangular,v opposed molded haii' shells formed of insulating material and eachA having abutting marginal portions, securing 1 means for maintaining said half shells in abutting relation whereby said shells form a closed chamber, a ilat substantially rectangular electrical heating element in said chamber, a plurality of integral spaced bosses arranged to extend inwardly from opposite marginal portions of Asaid shells and forming stopsat a considerable distance from the sides of said chamber between which lsaid heating element is disposed and by which said element is spaced from said margins of said shells, slabs of insulating material abutting the opposite at faces oi said heating element, and which, when said securing means are in operative position, are clamped between said heating element and the opposed faces of said half lshells to thereby hold said element against shifting, electrical contact receiving members permanently embedded in an end of one of said shells, and conductors leading from said element to said contact receiving members.

2. In an electric heating pad, a pair of shallow substantially rectangular, opposed molded half shells formed of insulating materialv and, .'e'nch having abutting marginal portions, a plupleting through the engaging contacts 48 and 50 f lity of integra-l, spaced bosses arranged to exlend inwardly from opposite side margins of said y, alf shells, Ithreaded bushings secured in the bossesV of one of said half shells, threaded securing devices passing through the corresponding bosses of said. other half shells and engaging in 'sad bushings to dra-w said abutting margins of said half shells together and form therebetween a closed chamber, a hat substantiallyrectangular v:electrical heating element, said bosses on said shells having opposed inwardly facing stops between which said heating element may .be disposed in operative position, slabs of slightly compressible, insulating material in face to face contact with the opposite faces o'f said heating element and which, when said half shells are secured together, are compressed fiatwise betweensaid heating element and the opposed half shells to thereby hold said element between said slabs4 vagainst shifting, electrical conductors extending from said heating element to an end of said shell,

and means for detachably connecting a source of electric current to said conductors for heating said element.

3. In an electric heating pad, a pair of shallow` substantially rectangular, opposed molded half shells formed of insulating material and each having abutting marginal portions and Substantially flat side walls, securing means for maintaining sad half shells inA abutting relation whereby said shells form a closed chamber, a flat substantially rectangular electrical heating element of considerably smaller lengthwise and transverse dimensions than the lengthwise andv crosswise inside dimensions of said chamber, relatively heavy slabs of heat insulating material of approximately the same length and width as that of said heating element disposed in face to face relation with the opposite faces of said element and substantially in parallel relation to said ilat side walls of said half shells, and relatively narrow, widely spaced strips of slightly compressible material engaging between said slabs and said opposed flat side walls of said half shells, whereby when said shelis are secured together, said strips will act to clamp said slabs and said heating element in position with a substantial air space surrounding said slabs and said element, opposed, spaced bosses extending into said chamber from the opposite marginal portionsof said half shells the inner ends of which l ranged between said means in said shell for bosses iorm stops between which said element and said slabs are disposed for spacing the same from the side margins of said shell, a thermostat unit mounted in said chamber in spaced relation to said heating element and to the side and end marginal portions of said shell, and electrically coupling said heater to said thermostat and said thermostat to a source of electric current at the outside of said shell.

4. In an electric heating pad, a pair of shallow substantially rectangular, opposed molded half shells formedv of insulating material and each having abutting marginal portions, securing means for maintaining said half shells in abutting relation whereby said shells form a closed chamber, a fiat substantially rectangular electrical heating. element in said chamber, a plurality of integral spaced bosses arrangedto extend inwardly from opposite marginal portions of said shells and forming stops at a considerable distance from said margins and between which said heating element is disposed and by which said element is spaced from said margins of said shells, a body of insulating' material arheating element and each of said half shells, means for spacing said material from the inner faces of said shell to provide an air space about said heating element and said material, means for clamping said element and said material in such spaced relation, one of said half shells having at one end thereof a pair of permanently embedded and insulated contact sleeves into which the contacts of an electric plug may be removably' engaged, and a thermostat mounted in xed position entirely within said chamber in spaced relation to said element, to said marginal portions of said shells and to said sleeves, and electrical conductors in said shell operatively connecting said thermostat with said element and with said sleeves.

5. In an electric heating pad, a pair of shallow substantially rectangular, opposed molded half shells formed of insulating material and each having abutting marginal portions, securing means for maintaining said half shells in abutting relation whereby said shells form a closed chamber, a fiat substantially rectangular electrical heating element in said chamber, a plurality of integral spaced bosses arranged to extend inwardly fromopposite marginal portions oi said heating element is element yis spaced from shells, means for insulating said element from said half shells, an integral boss formed at an fend of one of said half shells and projecting away from the margins of that half shell towards the other half shell, contact sleeves permanently embedded in said boss and extending from its outer face 'to the inside of said half shell for the reception of and attachment to the pad of conductors from a source of current, and said other halfl shell having a recess in its adjacent marginal portion forming a seat for the reception of the projecting portion of said end boss, a thermostat mounted in said shell, and means for electrically connecting said thermostat to said heating element and to said contact sleeves.

WILLIAM W. SMITH. 

